Ans. LOUDNESS
It is the characteristics of sound by which loud and feint sounds can be distinguished.
INTENSITY OF SOUND -
Sound energy passing per second through a unit area held perpendicular to
Solid direction of propagation of sound waves is called intensity of sound.
Unit: The SI unit of intensity of sound is watt per square metre (Wm ).
TaWeH.2
Sources of Sound
Intensity (WnT2)
Intensity level (dB)
Nearby jet airplane
103
150
Jackhammer / Fast
101
130
Train Siren
10°
120
Lawn mover
10^
100
Vacuum cleaner
1CT5
70
Mosquito buzzing
io-8
40
Whisper
to-9
30
Rusting of leaves
io~11
10
Faintest audible
ft *5
sound i.e. Threshold
10~12
0
Relation Between Loudness and Intensity of Sound
The loudness (L) of a sound is directly proportional to the logarithm of intensity.
i.e. L oc log I
or L=Klogl ...... (1)
where K is constant of proportionality.
Let L0 be the loudness of the faintest audible sound of intensity I0 and L be the loudness of an unknown sound of intensity 1, then by Eq. (1), we can write
L0 = KlogI0 ...... (2)
Subtracting Eq. (1) from Eq. (2), we get
L-L0 = KlogI-Klogl0 = K (log 1 - log 10) Since ( log a - log b - log t), therefore
L-L0=Klogf
Equation (3) give%the relation between loudness and intensity of sound.